In this connection, each rotor blade is fastened to the hub with a very large number of screws. It is therefore necessary for the assembly to align the rotor blade exactly to the bearing surface and to the hole pattern.
For this purpose, the rotor blade in accordance with the prior art is fastened to the hook block of a crane by means of a holding apparatus and is then raised into its assembly position. Due to the large exposed surface of the rotor blades, even small gusts of wind have a large effect on the position of the rotor blade. It is therefore always necessary in accordance with the prior art to wait for a time window in which no unacceptably high wind speeds can occur. This is all the more irritating since it is actually an objective to erect a wind power installation in regions which are particularly exposed to wind. This frequently causes a substantial time loss, which increases the assembly period and thus the costs for the expensive work equipment.